This invention relates to a lathe and more particularly to a lathe for machining balloon-shaped pockets in a workpiece.
In the manufacture of large integral turbine rotors a plurality of internal balloon-shaped pockets are machined in large diameter forgings to shape the turbine rotor. To machine these pockets 13 different offset tools were utilized to machine just one side of the balloon-shaped pocket and opposite hand tools were required for machining the other side of the balloon-shaped pocket. Thus a total of 26 different offset tools were utilized. Time required for tool changes during the machining was appreciable. Another problem was that every juncture of segments machined by different tools was a stress riser, which required polishing to remove the stress riser. The balloon-shaped pockets were very difficult to machine, particularly because finish requirements precluded any steps, undercuts or chatter marks, which could produce stress risers, which enhance the possibility of stress corrosion, as the environment in which the turbine rotor operates is one which leads to stress corrosion.